Ball valves are well known in the art, and a highly successful commercially available ball valve is described in U.S. Pat. No. 4,685,488 issued to Corbin et al. and owned by the assignee of the present invention, the entire disclosure of which is fully incorporated herein by reference.
Ball valves that use polymers for the ball packing material are usually limited in their rated or specified high and low temperature operating ranges at rated pressure. This is because the packing material expands and contracts at a different rate than other valve components which typically are made of stainless steel. At higher temperatures the packing material softens and tends to flow or creep and may become permanently deformed or otherwise damaged during valve actuation at higher temperature. This damage to the packing can result in leakage, especially when the valve returns to ambient temperature. At colder temperatures, the packing material becomes harder and stiffer and there may also, in some cases, be a decreased sealing stress on the packing due to packing shrinkage at lower temperatures. This loss of stress can produce leakage at lower temperatures. Although it is known to incorporate live load packing techniques into ball valves to increase the rated operating temperature range of the valve, the overall improvement is still limited by the temperature response characteristics of the packing material itself.
The need continues to exist for a ball valve having a polymer type ball packing material with increased rated operating temperature range and temperature cycling performance at rated pressure.